The present invention relates to a power amplifier, and more particularly to a protection circuit provided therein.
The power amplifier is generally provided with a speaker protection circuit for protecting loudspeakers and with an amplifier protection circuit for protecting the power amplifier itself, in case of malfunction. A typical speaker protection circuit has a speaker protective relay provided between the output terminal of the power amplifier and the loudspeaker. Upon generation of a DC voltage at the output terminal of the power amplifier, contacts of the relay are opened, thereby cutting off the connection between the amplifier and the speaker. However, the relays are costly, and moreover, cause the sound quality to decrease.
The amplifier protection circuit has a detecting means for detecting abnormalities of supply voltages at various stages of the power amplifier. The amplifier protection circuit comprises a relay or a fuse provided at the primary side of the power transformer. The contacts of the relay are opened when an abnormality is detected. Alternatively, the fuse is melted by an abnormal current to shut off the power supply circuit. A plurality of fuses for respective essential circuits are further provided at the secondary side of the transformer. Since the primary side fuse is set so as not to melt when the power amplifier generates an output of the rated output, the primary side fuse does not melt when an abnormality in an auxiliary circuit such as a voltage amplifier occurs. Therefore the secondary side fuses are provided to protect each circuit of the auxiliary circuit.
These fuses renders the construction of the circuit complicated and hence increases cost.